Karlsruhe, March 19, 2010. PTV's transportation experts will be presenting for the first time their latest development at Intertraffic in Amsterdam, 23rd - 26th March 2010: the link between the handbook of emission factors (HBEFA) and the transportation planning software VISUM.

To avoid traffic-related pollution, it is important to know the source and amount of pollutants emitted. The new method integrated into VISUM calculates all relevant pollutants and therefore enables traffic planners to address environmental issues using traffic planning tools. Traffic planning and environmental planning are thus moving even closer together.

According to the EU-Council Directive 1999/30/EG the annual average concentration of NO2should not exceed 40 µg/m³ in inner-city areas as of 2010. However, this value is often higher in areas affected by traffic. Thomas Haupt, member of the Board of Directors of PTV, therefore emphasises: "The EU-Directive on emission levels urgently requires traffic-related measures in order to conform to the limit values, in particular those for NO2levels. The new module now provides planning security and an officially recognised method for the calculation of pollutants. The authorities in charge must now start with the relevant analyses and introduce effective emission control measures." And he adds: "The development of the module was also based on the knowledge and expertise of PTV's logistics experts who use the component for climate neutral transport planning."

European standard: the handbook of emission factors

More than ten years ago the environmental agencies of Germany, Switzerland and Austria pooled their resources to compile a comprehensive database of emission factors. Recently the handbook of emission factors (HBEFA) underwent a major revision. The emission factors were updated to take into account new engine concepts and emission standards, and the traffic situations for which emission factors are published were re-structured more systematically. Moreover Sweden, Norway and France joined the consortium, so that the revised HBEFA is on its way to become a truly European standard. With those recent developments HBEFA perfectly complements VISUM for emission modelling.

Mapping the fleet makes traffic planning easier

Normally, demand models distinguish only a very small number of different vehicle types or transportation systems, often only cars and trucks. However, this is much to aggregate for emission calculations. Traffic-related emissions are based on a mix of various vehicle types, which behave similarly in terms of demand modelling, but have completely different emission factors.

Therefore, HBEFA comes with a ready-made vehicle fleet composition for different countries and years. For a national model of a region in Austria, the planner can map the VISUM transportation system “Car” to the HBEFA standard fleet mix “Car Austria 2015”, which is then composed of dozens of specific vehicle types. The macroscopic transportation planning software VISUM linked to HBEFA 3.1 thus significantly simplifies life for transportation planners.

Well-structured traffic situations

Emission factors depend not only on the vehicle type, but also on the traffic situation in which the vehicle is operating. Each traffic situation is defined by four descriptors, three of which relate to facility type and location (urban / rural, functional road class, free-flow speed). The fourth descriptor (Level of Service, LOS) is a qualitative four-step scale from free flow to traffic jam.

With these mappings in place, emission calculation becomes a very easy post-processing step of an assignment result from the demand model. For each network link VISUM disaggregates the volume to the HBEFA fleet mix, looks up the traffic situation and its emission factor, corrects for gradient, and multiplies. Even cold start emissions can be taken into consideration and be spatially distributed.

Link to immissions

The calculation of emissions is often not the end of the processing pipeline. In order to compare their environmental impact against thresholds imposed by legislation, they have to be converted to immissions first. This conversion, taking into account dispersal around detailed 3D topography and air chemistry, is the realm of specialised software. Open GIS standards ensure interoperability. So users can easily export emissions in the form of ESRI Shapefiles to any GIS-enabled immission model.